1. Field of the Invention
This invention relates to an electric type power assist steering device for a vehicle using an electric motor as a power source to reduce or assist the steering force of the steering wheel of the vehicle.
2. Description of the Prior Art
There are steering devices of the manually operated type and of the power-assisted type. In devices of the latter type, the steering power source reduces or assists the steering force. The power assist steering devices are further grouped into the electric type and the hydraulic type.
The electric type power steering device, as compared with the hydraulic type power assist steering device, is advantageous in that it does not require an oil pump as a power source connected to the engine and therefore there is no loss of engine horsepower; there is no possibility of leakage, contamination, deterioration or the like of hydraulic operating oil; maintenance is easy because operating oil is not used; hydraulic piping is not necessary, only electric wiring being required and thus assembly is easy; and an inexpensive system is possible because a highly accurate and delicate device such as an oil pressure control valve is not necessary.